1. Field of the Invention
This invention relates to switching means for use on-board a spacecraft.
2. Description of the Prior Art
Typically, a spacecraft such as a communications satellite has at least one receiving antenna, signal switching and amplifying means, and at least one transmitting antenna.
In order to provide the necessary transmitted signal power, it is usual to de-multiplex (hereinafter F.D.M) the uplink frequency division multiplex (shown schematically in FIG. 1) and amplify the individual narrow band channels which could, for example, be television channels, rather than amplify the broad band F.D.M. signal.
Redundancy is provided for in satellites and, for this reason, a larger number of narrow band amplifiers is provided compared with the number of active signal channels, and the repeater must contain redundancy switches to enable a failed narrow band amplifier to be substituted by a previously unused (redundant) one.
In general, the uplink frequency division multiplex will contain a larger number of frequency slots than active channels. Thus, for example, the F.D.M. could consist of 32 frequency slots but only 16 slots could be active. The on-board signal processing apparatus must therefore be provided with selection switches to enable the desired channels to be selected out of the larger number of de-multiplexed slots.
However, the flexibility provided by known selection switches is restricted. Typically, the uplink F.D.M. signal slots will be conceptually arranged in pairs, such that either one of each pair may be selected on-board the satellite. The disadvantage of this is that, for reasons of convenience, it might be desired to select both signal slots of a pair at the same time.
The invention provides switching means for use on-board a spacecraft, comprising a set of switches for connection between a number of possible r.f. channel slots and a smaller number of active r.f. signal paths, wherein at least two of the switches each have a first port, for connection to a respective channel slot, which is selectively connectable to a second port, for connection to an r.f. signal path, or to an additional port connected to an additional port of the other switch, so that the channel slot associated with each switch is connectable to the r.f. signal path associated with the switch or, via the switch interconnection, to the r.f. signal path associated with the other switch.
This arrangement of switches provides flexibility in connecting different channel slots along different signal paths. Both signal paths could be active or either could be active resulting from a signal in either channel slot.
The two switches may each have two additional ports to which the first port is selectively connectable, each additional port of each switch being connected to an additional port of another switch. In this way, the channel slot associated with each switch can be fed along at least three r.f. signal paths.
Advantageously a further set of switches is provided for connection between the active r.f. signal paths and selected ones of a greater number of r.f. amplifiers. Preferably, at least two of the further set of switches each have at first port, for connection to a respective r.f. signal path, which is selectively connectable to a second port, for connection to a respective r.f. amplifier, or to an additional port connected to an additional port of the other switch, so that the r.f. signal path associated with each switch is connectable to the r.f. amplifier associated with that switch or, via the switch interconnection, to the r.f. amplifier associated with the other switch. The further set of switches may be used to switch in a redundant amplifier, for example, in order to replace a malfunctioning amplifier but, in conjunction with the first-mentioned set of switches, the further set may also be used to select a particular channel slot while equally the first-mentioned set may be used to replace a malfunctioning amplifier. When both sets of switches are used, different amplifiers may be made redundant over the life of the satellite. This is not possible with existing sets of redundancy switches.
Switching means for use in a repeater on-board a satellite will now be described, by way of example with reference to the accompanying drawings, in which: